1. Field of the Invention
The present invention relates to a gas recovery unit in which a Chemical Vapor Deposition ("CVD") device is provided which is equipped with a gas introduction portion having an inert gas supply path for supplying a diluting inert gas, and a cleaning gas supply path for supplying a cleaning gas, each connected therewith, and equipped with an exhaust gas discharge portion for releasing an exhaust gas. The present invention also relates to a gas recovery unit in which an etching device is provided which is equipped with a gas introduction portion having an inert gas supply path for supplying a diluting inert gas, and an etching gas supply path for supplying an etching gas, each connected therewith, and equipped with an exhaust gas discharge portion for releasing an exhaust gas.
2. Description of the Related Art
In a gas recycle unit in which a CVD device is provided, the CVD is equipped with a gas introduction part having an inert gas supply path for supplying a diluting inert gas and a cleaning gas supply path for supplying a cleaning gas, each connected with the CVD device. The CVD device is further equipped with an exhaust gas discharge portion for releasing an exhaust gas, foreign matters such as silicon dioxide (SiO.sub.2), polysilicon, silicon nitride, metal silicide and amorphous silicon which are produced in said CVD device. It is therefore necessary to remove these foreign matters from the inside of the CVD device because they may have an adverse influence upon products in the CVD device. Accordingly, the introduction of a cleaning gas into the CVD device has been used to convert these foreign matters to volatile substances and to remove them. Namely, if a chemical compound, for example nitrogen trifluoride (NF.sub.3), which can react with these foreign matters so that they are converted to gaseous components, is introduced into said CVD device, silicon dioxide (SiO.sub.2) will be removed from the CVD device as silicon fluoride (SiF.sub.4), converted therefrom by nitrogen trifluoride (NF.sub.3). In the event that excess cleaning gas remains in the CVD device because it has not completely reacted with the foreign matter, it may be mixed in with the exhaust gas. Especially in a case where the cleaning gas is harmful, a gas recovery unit for recovering the cleaning gas has been proposed because the cleaning gas must be made harmless.
Additionally, in an etching device for bringing an etching gas which will react with a semiconductor film or the like into contact therewith to carry out etching, it has been desirable to recover the etching gas for the same reason.
Thus, an art of liquefying and recovering a cleaning gas or an etching gas can be devised. However, it has been pointed out that it is uneconomical to dispose of this cleaning or etching gas after it is made harmless because such gases are usually expensive. It is therefore desirable to develop an art of effectively and economically utilizing these gases.